Nearly half a million cases of bacterial sepses are reported annually in the USA and approximately one third of the cases are fatal. Increasingly, metal regulation and transport are being found of great significance in a wide range of biological processes and disease states. It is difficult to overestimate the significance of iron as a limiting nutrient in microbial growth, as documented in this proposal. This project was the first to study the coordination chemistry aspects of siderophore-mediated iron transport. As it has evolved, increasingly the focus has shifted to include studies of the transport process itself, including receptor structure and function. The first example of a direct role of the human immune system in binding and inactivating siderophores was found in the structure of the enterobactin adduct of NGAL (now called siderocalin), a human protein secreted by neutrophils. We intend to characterize the role of siderophore-binding and inactivation by proteins of the human immune system (in collaboration with Dr. Roland Strong). The "siderophore shuttle" mechanism of microbial iron transport is a completely different kind of transport system first observed by this research group in Aeromonas hydrophila. A search will be made to characterize how widely spread this transport system is and further studies of the remarkable features of this mechanism will be made to probe the mechanism of the iron exchange, which is a key feature of this uptake system (in part in collaboration with Prof. Alain Stintzi). Little is known about the iron transport processes of Gram-positive (single cell membrane) bacteria. It is proposed that the transport systems of some Gram-positive bacteria be studied to see if they follow the same patterns of those of better-characterized Gram-negative organisms. One Gram-positive siderophore, corynebactin, is a close relative of the much better known catecholate siderophore enterobactin. The remarkable structure of corynebactin raises a number of questions about its function and what possible advantages it can confer on the producing organisms. These will be probed through a wide range of activities, from chemical synthesis of the compound through receptor binding studies and characterization of the receptor protein (in part in collaboration with Profs. Alain Stintzi and Phillip Klebba). The coordination structures of non-crystalline samples of siderophores and analogs will be proved using EXAFS (in collaboration with Dr. David Shuh) and magnetic behavior will be probed by Mossbauer studies (in collaboration with Prof. Matzanke).